Revert "[ClangImporter] Decide whether to import Objective-C pointer types as"

This reverts commit fd11d2e.

Author: hborla

lib/ClangImporter/ImportDecl.cpp

@@ -2796,6 +2796,16 @@ namespace {
                                       SourceLoc(), Name,
                                       Loc,
                                       /*genericparams*/nullptr, DC);
+
+      // Unwrap an explicit ExistentialType around the underlying type so that
+      // the typealias can be used in a generic constraint context.
+      //
+      // FIXME: We might want to push this down further into importType(), and
+      // once ExistentialType becomes mandatory in the future we want to wrap
+      // references to imported typealiases in Sema's resolveType() as well.
+      if (auto *existentialType = SwiftType->getAs<ExistentialType>())
+        SwiftType = existentialType->getConstraintType();
+
       Result->setUnderlyingType(SwiftType);
 
       // Make Objective-C's 'id' unavailable.

lib/ClangImporter/ImportType.cpp

@@ -1050,7 +1050,6 @@ namespace {
               if (memberTypes.empty())
                 hasExplicitAnyObject = true;
 
-              // Generic arguments are always imported as existential types.
               Type importedTypeArg = ExistentialType::get(
                   ProtocolCompositionType::get(
                       Impl.SwiftContext, memberTypes,
@@ -1183,6 +1182,9 @@ namespace {
             }
           }
 
+          if (bridgedType->isConstraintType())
+            bridgedType = ExistentialType::get(bridgedType);
+
           return { importedType,
                    ImportHint(ImportHint::ObjCBridged, bridgedType) };
         }
@@ -1203,9 +1205,9 @@ namespace {
           members.push_back(proto->getDeclaredInterfaceType());
         }
 
-        importedType =
+        importedType = ExistentialType::get(
             ProtocolCompositionType::get(Impl.SwiftContext, members,
-                                         /*HasExplicitAnyObject=*/false);
+                                         /*HasExplicitAnyObject=*/false));
       }
 
       // Class or Class<P> maps to an existential metatype.
@@ -1283,32 +1285,6 @@ static bool isCFAudited(ImportTypeKind importKind) {
   llvm_unreachable("Invalid ImportTypeKind.");
 }
 
-/// True if the type can be an existential type in this context.
-static bool isExistentialContext(ImportTypeKind importKind) {
-  switch (importKind) {
-  case ImportTypeKind::Abstract:
-  case ImportTypeKind::Typedef:
-    return false;
-  case ImportTypeKind::Value:
-  case ImportTypeKind::ObjCCollectionElement:
-  case ImportTypeKind::Variable:
-  case ImportTypeKind::Result:
-  case ImportTypeKind::Enum:
-  case ImportTypeKind::RecordField:
-  case ImportTypeKind::AuditedVariable:
-  case ImportTypeKind::AuditedResult:
-  case ImportTypeKind::Parameter:
-  case ImportTypeKind::CompletionHandlerResultParameter:
-  case ImportTypeKind::CFRetainedOutParameter:
-  case ImportTypeKind::CFUnretainedOutParameter:
-  case ImportTypeKind::Property:
-  case ImportTypeKind::PropertyWithReferenceSemantics:
-    return true;
-  }
-
-  llvm_unreachable("Invalid ImportTypeKind.");
-}
-
 /// Turn T into Unmanaged<T>.
 static Type getUnmanagedType(ClangImporter::Implementation &impl,
                              Type payloadType) {
@@ -1574,11 +1550,6 @@ static ImportedType adjustTypeForConcreteImport(
 
   assert(importedType);
 
-  if (importedType->isConstraintType() &&
-      isExistentialContext(importKind)) {
-    importedType = ExistentialType::get(importedType);
-  }
-
   if (importKind == ImportTypeKind::RecordField &&
       importedType->isAnyClassReferenceType() &&
       !importedType->isForeignReferenceType()) {

lib/PrintAsClang/DeclAndTypePrinter.cpp

@@ -1835,7 +1835,8 @@ class DeclAndTypePrinter::Implementation
 
   void visitExistentialType(ExistentialType *ET,
                             Optional<OptionalTypeKind> optionalKind) {
-    visitPart(ET->getConstraintType(), optionalKind);
+    visitExistentialType(ET, optionalKind,
+        /*isMetatype=*/ET->getConstraintType()->is<AnyMetatypeType>());
   }
 
   void visitExistentialMetatypeType(ExistentialMetatypeType *MT,